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Activation-induced cytidine deaminase, also known as AICDA and AID, is a 24 kDa enzyme which in humans is encoded by the ''AICDA'' gene.〔(【引用サイトリンク】 url = http://www.ncbi.nlm.nih.gov/sites/entrez?Db=gene&Cmd=ShowDetailView&TermToSearch=57379 )〕 It creates mutations in DNA〔(【引用サイトリンク】url=http://www.uniprot.org/uniprot/Q9GZX7 )〕 by deamination of cytosine base, which turns it into uracil (which is recognized as a thymine). In other words, it changes a C:G base pair into a U:G mismatch. The cell's DNA replication machinery recognizes the U as a T, and hence C:G is converted to a T:A base pair. During germinal center development of B lymphocytes, AID also generates other types of mutations, such as C:G to A:T. The mechanism by which these other mutations are created is not well-understood. In B cells in the lymph nodes, AID causes mutations that produce antibody diversity, but that same mutation process leads to B-cell lymphoma. == Function == This gene encodes a DNA-editing deaminase that is a member of the cytidine deaminase family. The protein is involved in somatic hypermutation, gene conversion, and class-switch recombination of immunoglobulin genes.〔 AID is currently thought to be the master regulator of secondary antibody diversification. It is involved in the initiation of three separate immunoglobulin (Ig) diversification processes: # Somatic hypermutation (SHM), in which the antibody genes are minimally mutated to generate a library of antibody variants, some of which with higher affinity for a particular antigen and any of its close variants # Class switch recombination (CSR), in which B cells change their expression from IgM to IgG or other immune types # Gene conversion (GC) a process that causes mutations in antibody genes of chickens, pigs and some other vertebrates. AID has been shown in vitro to be active on single-strand DNA, and has been shown to require active transcription in order to exert its deaminating activity. The involvement of Cis-regulatory factors is suspected as AID activity is several orders of magnitude higher in the immunoglobulin "variable" region than other regions of the genome that are known to be subject to AID activity. This is also true of artificial reporter constructs and transgenes that have been integrated into the genome. A recent publication suggests that high AID activity at a few non-immunoglobulin targets is achieved when transcription on opposite DNA strands converges due to super-enhancer activity. Recently, AICDA has been implicated in active DNA demethylation. AICDA can deaminate 5-methylcytosine, which can then be replaced with cytosine by base excision repair. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Activation-induced cytidine deaminase」の詳細全文を読む スポンサード リンク
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